Support serializing shadow DOM to MHTML

third_party/WebKit/Source/web/WebFrameSerializer.cpp

Index: third_party/WebKit/Source/web/WebFrameSerializer.cpp
diff --git a/third_party/WebKit/Source/web/WebFrameSerializer.cpp b/third_party/WebKit/Source/web/WebFrameSerializer.cpp
index 5ae9b75c24659cbfe022424e8fb66b0041688498..617dc042f62533923c43949939d4e0a137935756 100644
--- a/third_party/WebKit/Source/web/WebFrameSerializer.cpp
+++ b/third_party/WebKit/Source/web/WebFrameSerializer.cpp
@@ -34,6 +34,7 @@
 #include "core/InputTypeNames.h"
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
+#include "core/dom/shadow/ElementShadow.h"
 #include "core/frame/Frame.h"
 #include "core/frame/FrameSerializer.h"
 #include "core/frame/LocalFrame.h"
@@ -80,13 +81,17 @@ namespace blink {
 namespace {
 
 const int kPopupOverlayZIndexThreshold = 50;
+const char kShadowModeAttributeName[] = "shadowmode";
+const char kShadowDelegatesFocusAttributeName[] = "shadowdelegatesfocus";
 
 class MHTMLFrameSerializerDelegate final : public FrameSerializer::Delegate {
+  STACK_ALLOCATED()
   WTF_MAKE_NONCOPYABLE(MHTMLFrameSerializerDelegate);
 
  public:
-  explicit MHTMLFrameSerializerDelegate(
-      WebFrameSerializer::MHTMLPartsGenerationDelegate&);
+  MHTMLFrameSerializerDelegate(
+      WebFrameSerializer::MHTMLPartsGenerationDelegate&,
+      HeapHashSet<WeakMember<const Element>>&);
   ~MHTMLFrameSerializerDelegate() override;
   bool ShouldIgnoreElement(const Element&) override;
   bool ShouldIgnoreAttribute(const Element&, const Attribute&) override;
@@ -95,6 +100,7 @@ class MHTMLFrameSerializerDelegate final : public FrameSerializer::Delegate {
   bool ShouldSkipResource(
       FrameSerializer::ResourceHasCacheControlNoStoreHeader) override;
   Vector<Attribute> GetCustomAttributes(const Element&) override;
+  Node* GetAuxiliaryDOMTree(const Element&, Element**) const override;
 
  private:
   bool ShouldIgnoreHiddenElement(const Element&);
@@ -106,12 +112,16 @@ class MHTMLFrameSerializerDelegate final : public FrameSerializer::Delegate {
                                                 Vector<Attribute>*);
 
   WebFrameSerializer::MHTMLPartsGenerationDelegate& web_delegate_;
+  HeapHashSet<WeakMember<const Element>>& shadow_template_elements_;
   bool popup_overlays_skipped_;
 };
 
 MHTMLFrameSerializerDelegate::MHTMLFrameSerializerDelegate(
-    WebFrameSerializer::MHTMLPartsGenerationDelegate& web_delegate)
-    : web_delegate_(web_delegate), popup_overlays_skipped_(false) {}
+    WebFrameSerializer::MHTMLPartsGenerationDelegate& web_delegate,
+    HeapHashSet<WeakMember<const Element>>& shadow_template_elements)
+    : web_delegate_(web_delegate),
+      shadow_template_elements_(shadow_template_elements),
+      popup_overlays_skipped_(false) {}
 
 MHTMLFrameSerializerDelegate::~MHTMLFrameSerializerDelegate() {
   if (web_delegate_.RemovePopupOverlay()) {
@@ -202,6 +212,15 @@ bool MHTMLFrameSerializerDelegate::ShouldIgnoreAttribute(
     return true;
   }
 
+  // The special attribute in a template element to denote the shadow DOM
+  // should only be generated from MHTML serialization. If it is found in the
+  // original page, it should be ignored.
+  if (isHTMLTemplateElement(element) &&
+      attribute.LocalName() == kShadowModeAttributeName &&
+      !shadow_template_elements_.Contains(&element)) {
+    return true;
+  }
+
   // If srcdoc attribute for frame elements will be rewritten as src attribute
   // containing link instead of html contents, don't ignore the attribute.
   // Bail out now to avoid the check in Element::isScriptingAttribute.
@@ -329,6 +348,52 @@ void MHTMLFrameSerializerDelegate::GetCustomAttributesForFormControlElement(
   attributes->push_back(disabled_attribute);
 }
 
+Node* MHTMLFrameSerializerDelegate::GetAuxiliaryDOMTree(
+    const Element& element,
+    Element** enclosing_element) const {
+  DCHECK(enclosing_element);
+
+  const ElementShadow* shadow = element.Shadow();
+  if (!shadow)
+    return nullptr;
+  ShadowRoot& shadow_root = shadow->OldestShadowRoot();
+
+  String shadow_mode;
+  switch (shadow_root.GetType()) {
+    case ShadowRootType::kUserAgent:
+      // No need to serialize.
+      return nullptr;
+    case ShadowRootType::V0:
+      shadow_mode = "v0";
+      break;
+    case ShadowRootType::kOpen:
+      shadow_mode = "open";
+      break;
+    case ShadowRootType::kClosed:
+      shadow_mode = "closed";
+      break;
+  }
+
+  // Put the shadow DOM content inside a template element. A special attribute
+  // is set to tell the mode of the shadow DOM.
+  Element* template_element =
+      Element::Create(HTMLNames::templateTag, &(element.GetDocument()));
+  template_element->setAttribute(
+      QualifiedName(g_null_atom, kShadowModeAttributeName, g_null_atom),
+      AtomicString(shadow_mode));
+  if (shadow_root.GetType() != ShadowRootType::V0 &&
+      shadow_root.delegatesFocus()) {
+    template_element->setAttribute(
+        QualifiedName(g_null_atom, kShadowDelegatesFocusAttributeName,
+                      g_null_atom),
+        g_empty_atom);
+  }
+  shadow_template_elements_.insert(template_element);
+
+  *enclosing_element = template_element;
+  return &shadow_root;
+}
+
 bool CacheControlNoStoreHeaderPresent(
     const WebLocalFrameBase& web_local_frame) {
   const ResourceResponse& response =
@@ -414,7 +479,9 @@ WebThreadSafeData WebFrameSerializer::GenerateMHTMLParts(
   {
     SCOPED_BLINK_UMA_HISTOGRAM_TIMER(
         "PageSerialization.MhtmlGeneration.SerializationTime.SingleFrame");
-    MHTMLFrameSerializerDelegate core_delegate(*web_delegate);
+    HeapHashSet<WeakMember<const Element>> shadow_template_elements;
+    MHTMLFrameSerializerDelegate core_delegate(*web_delegate,
+                                               shadow_template_elements);
     FrameSerializer serializer(resources, core_delegate);
     serializer.SerializeFrame(*frame);
   }